An earlier filed patent application, U.S. Pat. Pub. 2014/0312716, the contents of which are incorporated herein by reference, describes a linear actuator. In its simplest form, the linear actuator includes a linear array of coils wound around a core of magnetically permeable material and an actuator assembly encircling the array of coils. The actuator assembly, which is made up of a linear array of ring magnets made of a permanent magnetic material, is arranged to move back and forth along the length of the array of coils under the control of signals that are applied to the coils. By applying appropriate signals to coils within the array, the position and movement of the actuator assembly can be controlled.
For such a linear actuator, it is useful to be able to accurately determine the location of the actuator assembly relative to the array of coils. The controller can use this positional information to determine which coils in the array to excite so as to optimally drive the movement of the actuator assembly and to accurately reposition the actuator assembly where desired. Typically, the information is determined by using an array of sensors that are mounted on the actuator. Two examples of such sensors that are mentioned in the earlier filed application are a linear potentiometer and a linear encoder.
This application describes an alternative approach to determining the location of the actuator assembly from measured electrical characteristics of the coils.